JSP&Servlet学习笔记----第1/2章

HTML(HyperText Markup Language)：超文本标记语言

HTTP(HyperText Transfer Protocol)：超文本传输协议

URL(Uniform Resource Locator)：统一资源定位符，以文字的方式来说明因特网上的资源如何取得。

URN(Uniform Resource Name)：代表某个资源独一无二的名称，如图书的ISBN。

URI(Uniform Resource Identifier)：URL和URN是URI的子集。

一个简单的html范例程序：

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>HTML范例</title>
</head>
<body>
    <form method="get" action="hello.do" name="sample">
        姓名：
        <input type="text" name="name">
        <br />
        <button>发送</button>
    </form>
</body>
</html>
HTML学习资源：http://www.w3school.com.cn/html/index.asp

HTTP：指架构在TCP/IP之上应用层的一种协议。它的两个特点：

1、无状态（stateless）通信协议。（无记忆性）

2、基于请求（request）/响应（response）模型。

客户端对服务器发出一个取得资源的请求，服务器将要求的资源响应给客户端，每次的联机只作一次请求/响应，是一种很简单的通信协议，没有请求就没有响应。

在HTTP 协议下，服务器是个健忘的家伙，服务器响应客户端之后，就不会记得客户端的信息，更不会去维护与客户端有关的状态，因此HTTP又称为无状态的通信协议。

浏览器在使用http发送请求，最重要的就是GET和POST。

GET：就是向服务器取得指定的资源。

POST请求：就是请求时发布(POST)信息给服务器。

对于两者如何进行选择？

1、get方式请求参数长度是有限的，过长的或者如文件上传应该使用post请求。

2、get请求参数会出现在地址栏。

3、get请求纯粹是为了取得资源，而不改变服务器上的资源的状态。而post相反。

对于java，JVM(java virtual machine)是java程序唯一认得的操作系统，其可执行文件为.class文件。

对于JSP/Servlet，Web容器是JSP/Servlet唯一认得的http服务器。

URL编解码：

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;

/**
 * Created by N3verL4nd on 2017/1/2.
 */


public class HelloWorld
{
    public static void main(String[] args) throws UnsupportedEncodingException {
        System.out.println(URLEncoder.encode("http://www.baidu.com", "UTF-8"));
        System.out.println(URLDecoder.decode("%3A", "UTF-8"));
    }
}
URL编码针对的字符是UTF-8编码的8个位数值。

对于ascii字符使用1个字节，非ascii如中文使用3个字节。

import java.io.UnsupportedEncodingException;
import java.net.URLDecoder;
import java.net.URLEncoder;

/**
 * Created by N3verL4nd on 2017/1/2.
 */
public class HelloWorld
{
    public static void main(String[] args) throws UnsupportedEncodingException {
        System.out.println(URLEncoder.encode("我", "UTF-8"));
        System.out.println(URLDecoder.decode("%E6%88%91", "UTF-8"));
    }
}
HTTP规范下的URL编码，并不限使用UTF-8，例如在一个BIG5网页中，若窗体使用get发送中文，则是使用BIG5编码的参数。

System.out.println(URLEncoder.encode("我", "BIG5"));

第一个Servlet程序(打印http header)：

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

/**
 * Created by N3verL4nd on 2017/1/4.
 */
@WebServlet(name = "testServlet",urlPatterns = {"/test.do"})
public class testServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        out.println("<html>");
        out.println("<head>");
        out.println("<title>TEST</title>");
        out.println("</head>");
        out.println("<body>");

        out.println("<h1>Hello World</h1>");

        out.println("</body>");
        out.println("</html>");
        out.close();
    }
}

/test.do
/Servlet
/Servlet/test.do host:localhost:8080
connection:keep-alive
upgrade-insecure-requests:1
user-agent:Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.87 Safari/537.36
accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
accept-encoding:gzip, deflate, sdch, br
accept-language:zh-CN,zh;q=0.8
cookie:JSESSIONID=CDD8329D5BB881383911AC4CFAB4A159; Idea-e643fc73=b918ddfe-f8fa-43a0-b608-e1670a29b80a

@WebServlet(name = "testServlet",urlPatterns = {"/test.do"})
这表示该Servlet名称为testServlet，当请求的URL是/test.do，如http://localhost:8080/Servlet/test.do就会由testServlet处理。 
HttpServletRequest

代表请求对象，封装了HTTP请求信息。

HttpServletResponse
代表对客户端的响应。

Servlet的编译(需servlet-api.jar。位于D:Tomcatapache-tomcat-9.0.0.M15lib)：



一个简易的Servlet程序对应的文件目录结构如下：

E:MyDocumentDesktopjspRunwebWEB-INF>tree /f
文件夹 PATH 列表
卷序列号为 025427CF 32D1:7CF3
E:.
│  web.xml
│
├─classes
│      testServlet.class
│
└─lib


E:MyDocumentDesktopjspRunwebWEB-INF>
部署：

将web.war拷贝到webapps目录下（D:Tomcatapache-tomcat-9.0.0.M15webapps ）

运行bin目录下的startup.bat


servlet、genericservlet、httpservlet之间的关系：


package javax.servlet;
import java.io.IOException;
public interface Servlet {
    public void init(ServletConfig config) throws ServletException;
    public ServletConfig getServletConfig();
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;
    public String getServletInfo();
    public void destroy();
}

package javax.servlet;
import java.io.IOException;
import java.util.Enumeration;
public abstract class GenericServlet implements Servlet, ServletConfig,
        java.io.Serializable {

    private static final long serialVersionUID = 1L;

    private transient ServletConfig config;
    public GenericServlet() {
        // NOOP
    }
    @Override
    public void destroy() {
        // NOOP by default
    }
    @Override
    public String getInitParameter(String name) {
        return getServletConfig().getInitParameter(name);
    }
    @Override
    public Enumeration<String> getInitParameterNames() {
        return getServletConfig().getInitParameterNames();
    }
    @Override
    public ServletConfig getServletConfig() {
        return config;
    }
    @Override
    public ServletContext getServletContext() {
        return getServletConfig().getServletContext();
    }
    @Override
    public String getServletInfo() {
        return "";
    }
    @Override
    public void init(ServletConfig config) throws ServletException {
        this.config = config;
        this.init();
    }
    public void init() throws ServletException {
        // NOOP by default
    }

    public void log(String msg) {
        getServletContext().log(getServletName() + ": " + msg);
    }
    public void log(String message, Throwable t) {
        getServletContext().log(getServletName() + ": " + message, t);
    }
    @Override
    public abstract void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException;
    @Override
    public String getServletName() {
        return config.getServletName();
    }
}
package javax.servlet.http;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Enumeration;
import java.util.ResourceBundle;
import javax.servlet.DispatcherType;
import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public abstract class HttpServlet extends GenericServlet {
    private static final long serialVersionUID = 1L;
    private static final String METHOD_DELETE = "DELETE";
    private static final String METHOD_HEAD = "HEAD";
    private static final String METHOD_GET = "GET";
    private static final String METHOD_OPTIONS = "OPTIONS";
    private static final String METHOD_POST = "POST";
    private static final String METHOD_PUT = "PUT";
    private static final String METHOD_TRACE = "TRACE";
    private static final String HEADER_IFMODSINCE = "If-Modified-Since";
    private static final String HEADER_LASTMOD = "Last-Modified";
    private static final String LSTRING_FILE =
        "javax.servlet.http.LocalStrings";
    private static final ResourceBundle lStrings =
        ResourceBundle.getBundle(LSTRING_FILE);
    public HttpServlet() {
        // NOOP
    }
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException
    {
        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_get_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }
    protected long getLastModified(HttpServletRequest req) {
        return -1;
    }
    protected void doHead(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        if (DispatcherType.INCLUDE.equals(req.getDispatcherType())) {
            doGet(req, resp);
        } else {
            NoBodyResponse response = new NoBodyResponse(resp);
            doGet(req, response);
            response.setContentLength();
        }
    }
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws ServletException, IOException {

        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_post_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        }
    }
    ...
}
Servlet接口：定义了Servlet应当有的基本行为，所有的Servlet程序都必须实现Servlet接口（GenericServlet或者HttpServlet）。

GenericServlet：实现了Servlet接口，没有规范任何与HTTP相关的方法，而是由继承它的HttpServlet来定义。

HttpServlet的service方法流程：

protected void service(HttpServletRequest req, HttpServletResponse resp)
    throws ServletException, IOException {

    String method = req.getMethod();

    if (method.equals(METHOD_GET)) {
        long lastModified = getLastModified(req);
        if (lastModified == -1) {
            // servlet doesn't support if-modified-since, no reason
            // to go through further expensive logic
            doGet(req, resp);
        } else {
            long ifModifiedSince;
            try {
                ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
            } catch (IllegalArgumentException iae) {
                // Invalid date header - proceed as if none was set
                ifModifiedSince = -1;
            }
            if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                // If the servlet mod time is later, call doGet()
                // Round down to the nearest second for a proper compare
                // A ifModifiedSince of -1 will always be less
                maybeSetLastModified(resp, lastModified);
                doGet(req, resp);
            } else {
                resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            }
        }

    } else if (method.equals(METHOD_HEAD)) {
        long lastModified = getLastModified(req);
        maybeSetLastModified(resp, lastModified);
        doHead(req, resp);

    } else if (method.equals(METHOD_POST)) {
        doPost(req, resp);

    } else if (method.equals(METHOD_PUT)) {
        doPut(req, resp);

    } else if (method.equals(METHOD_DELETE)) {
        doDelete(req, resp);

    } else if (method.equals(METHOD_OPTIONS)) {
        doOptions(req,resp);

    } else if (method.equals(METHOD_TRACE)) {
        doTrace(req,resp);

    } else {
        //
        // Note that this means NO servlet supports whatever
        // method was requested, anywhere on this server.
        //

        String errMsg = lStrings.getString("http.method_not_implemented");
        Object[] errArgs = new Object[1];
        errArgs[0] = method;
        errMsg = MessageFormat.format(errMsg, errArgs);

        resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
    }
}
当请求到来时，容器会调用Servlet的service()方法。





Keep it simple!
作者：N3verL4nd
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原文地址：https://www.cnblogs.com/lgh1992314/p/6616253.html